Autoimmune diseases affect approximately 5% of the population and cause significant morbidity and mortality. The exact cause of most autoimmune diseases is unknown but is thought to be due to a combination of environmental and genetic factors. One critical mechanism humans use to prevent autoimmune disease is the process of central tolerance whereby self-reactive T cells are deleted in the thymus. The importance of central tolerance is highlighted by autoimmune polyglandular syndrome type I (APS1), an autosomal recessive monogenic autoimmune syndrome in which affected patients develop multi-organ autoimmunity. The defective gene in APS1 is the autoimmune regulator (AIRE) gene which is responsible for the expression of thousands of tissue-restricted antigens (TRAs) by medullary thymic epithelial cells (mTECs). mTECs present TRAs to developing T cells in the context of MHC class II, enabling the deletion of autoreactive T cells. While Aire is known to be critical for TRA gene expression, the exact mechanism Aire uses to induce TRA genes is unknown. Further understanding of Aire's mechanism of action will yield insights into the pathogenesis of APS1 as well as other more common autoimmune diseases which have recently been linked to AIRE such as rheumatoid arthritis. This career development proposal has two primary goals. First, the candidate outlines a 5-year career development plan to establish an independent research program. Highlights of this plan include mentorship by Dr. Mark Anderson, a committee structured to provide both scientific and career advice during the candidate's progress, didactic coursework, meetings to supplement local opportunities for scientific enrichment and networking, and finally workshops on laboratory management and professional skills. Second, the candidate outlines a 5-year research strategy to examine fundamental questions related to Aire's mechanism of action. Recent studies have identified two novel Aire-interacting proteins previously known to be involved in the epigenetics of gene repression: activating transcription factor 7 interacting protein (ATF7ip) and methyl CpG binding protein 1 (MBD1). Aire's interaction with the ATF7ip/MBD1 protein complex is critical for TRA gene expression and data published in a recent Nature Immunology paper has shown that Aire binds MBD1 for specificity in inducing TRA gene expression. Furthermore, consistent with MBD1's role in TRA gene expression, Mbd1-/- mice develop autoimmunity. Aim 1 will examine the cellular mechanism of MBD1 in immunotolerance. Aim 2 will interrogate the in vivo role of ATF7ip in TRA gene expression and the prevention of autoimmunity. Aim 3 seeks to further define the molecular mechanisms Aire uses to target TRA genes in vivo. The candidate is an MSTP graduate and pediatric rheumatologist at the University of California, San Francisco (UCSF). Though the candidate has a background in immunology, the areas of prior study and techniques previously employed are distant from his current scientific focus. He would, therefore, benefit from the structured period of mentorship and training outlined in the proposal. After completion of the training period, the candidate will continue to develop an independent research program at an academic medical center with the long-term goal of understanding the underlying mechanisms of autoimmune disease. UCSF provides an ideal environment for the training of pediatric physician-scientists. The UCSF Department of Pediatrics has a long track record of fostering the career development of young faculty. In addition, the UCSF immunology program has a unique breadth of immunological expertise with a number of investigators who are leaders in their respective fields. In summary, this proposal will foster the continued development of the candidate's clinical and scientific portfolio. Upon completion of the proposal, the candidate will likely have made a number of original contributions to our understanding of central tolerance and autoimmune disease. The candidate will also be positioned to compete for further funding opportunities as he develops an independent research program.